A colloquialism generally referring to an alcohol abuser's sobering up time. Can also be used as a general reference to refraining from any bad habit, i.e. diet or drug usage. Closely related to fell off the wagon.

1. "Hey Bill, you wanna do whiskey shots tonight?" "Sorry Bob, I'm on the wagon."
2. "Hey Jim, you sticking to that Atkins diet thing?" "Yup, I'm still on the wagon."